Tidy up gemspec

I was tackling this issue:

  https://github.com/causes/mock_redis/issues/64

but had a mid-air collision with Aaron who was working on it
simultaneously here:

  https://gerrit.causes.com/26336

I've removed the hunk that adds the license, and am pushing the nearby
clean-up changes that I'd made (double quotes to singles, wrapped long
lines).

Change-Id: I0b9e00bfe0db01c5d7e083e4fa0a05ff44b8e634
Reviewed-on: https://gerrit.causes.com/26337
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Aaron Neyer <aaron.neyer@causes.com>